The ability to control the various fouling issues for industrial water systems has long been sought. Fouling refers to biofilm including its formation, organic deposits including their formation, metal corrosion, surface discoloration or any other adverse consequences in industrial systems that are directly, indirectly or otherwise due to the presence or action of microorganisms that are freely floating in a liquid or are associated with a surface of such industrial water system or inorganic deposits including their formation due to the concentration and precipitation of compounds present in hard water of such industrial water system. Organic deposits include non-viable microbial cells and their associated organic products, such as cellular proteins, lipids, and nucleic acids. In particular, organic deposits include polysaccharides. Compounds which disperse such organic deposits are referred to as biodispersants. To control such fouling refers to prevention, reduction or removal of such fouling.
Various methods to have a slow release formulation for water systems have been attempted that would provide: 1) continuous applications to an industrial water system by non-mechanical means (i.e., without the use of pumps, an eductor or dispersing apparatus); 2) relatively constant concentrations of the active compound in spite of the water turnover in the industrial water system over a long time; and 3) ease of treatment relative to manual introduction of liquids to minimize environmental and personnel exposure issues.
To provide those objectives, slow release tablets of various types have been tried. For example, a tablet using 2,2-dibromo-3-nitrilopropionamide (DBNPA) as an active ingredient biocide, hydrophilic polymer and compression agent has been made (see U.S. Pat. No. 4,800,082). However, there are no other actives in this formulation. Because there are no biodispersants, scale inhibitors or corrosion inhibitors used, those would need to be added separately as required for the specific water conditions. The active ingredient DBNPA, at alkaline pH, such as pH˜9 in industrial water system conditions, is degraded under these end use conditions in a few minutes.
U.S. Pat. No. 4,816,061 discloses a method for biocide use at an alkaline pH (7.5-12) or high water hardness using an n-decylthioethylamine as the active ingredient. There is no solid formulation or slow release method disclosed. There is no presence of other actives in one formulation mentioned. A typical dose of this patented composition is effective for 1-1.5 days in a typical cooling tower system. The active ingredient does not react with other typical water treatment ingredients which may be added.
In recirculating water systems U.S. Pat. No. 5,514,287 discloses a tablet composition containing a boron source material, a halogen source material, and glycoluril. The tablet is used in conjunction with a boron source material and a periodic addition of a chlorine source material, which are added directly to the water. This is a tablet formulation having only active ingredients that are quick dissolving and therefore is used to avoid the addition of liquid chemicals. There is no hydrophilic polymer present to control the release rate of the active ingredients. There are no scale inhibitors or corrosion inhibitors used so those would need to be added as required for the specific water conditions. The use of these patented tablets is for swimming pools. Such pH conditions for swimming pools are usually ˜7, while pH conditions for industrial water systems are more alkaline, such as pH 8 and above.
A multilayer tablet was made in U.S. Pat. No. 6,863,830 where there was a fast dissolving layer and a slow dissolving layer. Hydrophilic polymers are taught as binders but not used as control release agents. The examples show that the rate of dissolution is a property of the individual chemicals used or their mixtures; it is not based on any polymer matrix. Two layers are required to obtain the results. There is no discussion of alkaline pH conditions in the water systems they tested.
When a vehicle cooling system is the water source, a controlled release system was used in U.S. Pat. No. 6,607,694. It contains a core of active ingredients which may contain a hydrophilic polymer as a binder, and an insoluble coating that controls the rate of release. There is no biocide or organic deposit control actives that are needed for industrial water systems present.
At a NACE International Corrosion Conference in 2007, Paper No. 07069 disclosed using controlled release technology for cooling towers. Various diffusion methods were discussed but these tablets required a core of active (such as corrosion inhibitor and scale inhibitor) and a polymer coating which controlled the release rate for about 30 days. There was no biocide or organic deposit control agent present in the tablet, but it was added separately.
U.S. Pat. No. 5,603,941 describes a solid tablet comprising a biocide and biodispersant for industrial, household, and recreational water applications. The rate of dissolution is not described, but presumably is determined by the solubility of its chemical components. It does not have a hydrophilic polymer matrix to effect slow release, and there is no specification of the water that is to be treated, such as pH or hardness.
At the International Water Conference held on Oct. 28, 2008, paper number IWC-08-40 disclosed the use of a solid mixture of scale and corrosion inhibitors in the form of a tablet containing 100% active ingredient and thus had no hydrophilic polymer. The tablets are dissolved in water in a separate vessel and then the resultant solution is fed into the water system with automated pumps as needed. The active ingredients are not slowly released. Different formulations were used for hard and soft water applications.
U.S. Published Application 2006/0165745 discloses a tablet for sustained release in water systems. The tablet has a hydrophilic polymer and an active ingredient and requires a curing step to a specified water level by steaming the tablets or by setting them out at room temperature in humidity. This curing step that requires addition of water is stated to be important so that the tablet does not prematurely disintegrate during use. The release of the active ingredient occurs over 30 days. There is no discussion of the pH being alkaline in the water system or water hardness as found in industrial water systems.
Currently sold are solid forms of biocides with binders. These solids are then put into a closed chamber and water is introduced at a sufficient high pressure to erode the solid into smaller pieces or to dissolve it. Without this ablative action of the water these solids cannot be dissolved into the water system.
Clearly, it would be desirable to have several actives or one multifunctional active in one solid form, such as a tablet composition, which provides a sustained release over a long time, where multiple water cycles in a water circulation system are possible, under alkaline pH or high water hardness, and be effective against fouling in industrial water systems. Additionally, there are no such slow release compositions presently known that are effective to remove, to inhibit, and to control fouling in industrial water systems.